Retractable landing gear for aircraft



R. L. LEVY RETRACTABLE LANDING GEAR FOR AIRCRAFT April 8, 1952 3Sheets-Sheet 1 Filed May 27, 1946 April 8', 1952 R. L. LEVY 2,591,839

RETRACTABLE LANDING GEAR FOR AIRCRAFT Filed May 27, 1946 s Sheets-Sheet2 can") m \m April 8, 1952 R. LEVY RETRACTABLE LANDING GEAR FOR AIRCRAFT3 Sheets-Sheet 3 Filed May 2'7, A946 Patented Apr. 8, 1 952 OFFICE" ofSwitzerland;

, l plication Mayz'igf1946, Serial No; 672i5'1'0t I ln-FranceJanuarygi;1942? Section-1, Public Law ,690, August 8, 1946 Batentexpires January 7', 196.2. s

6 Claims. (CUBE-517 I Thewipresent invention; v relates to retractablelandingrgeartfor aircratt .and more particularly relates tor a control;system 7 governing l the re tractionand extension or lowering ofsuch-gear of the: in which the-movement. loinithe gear is effected byhydraulic means. SuchTanding gearcontrol systems .are generally knownwhich" previde locking meanslcooperable. with the .gear imaboth theretracted andr extended; position. However known. arrangements donotafford suflicient rsecurity-1mm safety since their operation for themost part 1 is: predicated upon. the condition of; the rhydzaulicqfluidgoverning theoperationo! the: gear; In: other wordslir there leakage inthe-1 fluid. -,circuit-ot -.th'e slandingog ear system and the lockingmeans: areebeing. dependentiupon. the samefluid circuit, the raisingandlowering means are; ineffective Thelsame c1rawbisicl':.can;v occur 7merely through a. dilatation of jth'ehfiuid in the circuit l.Theretorethe present inventionlhasfo'r a primary, object: to provideanlanding gear system-in which. tthenloc'kingcmeans is.v effective in.either the.,retra.oted or} the lowered .ior extended ipositionotthegears Thesystemmf the present inv ventioni'sloperativetojmaintain thegear jlocked inheither vot -itsextreme positionsveven if"there Jectthat-if "damage foccurred to the fluid; circuit white-the gearswere inretracted-condition they were thereby lowere'df Under; present dayflight op ration it is preferable to risk the so-call'edhellyeland'ing'with the gearsretracted-and retain the eflectattendant toretracted" gearsin order ,to providei-the aircraftwith maximumefliciency dnri'ngfii'ght. The system the present invention' conforms tothis conception of fli'ght'operatiomsince the'gears-once retracted arelocked and irtthe' fluid circuit disrupted the gears remain retracted.Additionallyif the *gearsare lowered when -th'e-Yrcuit1=is disrupted-the same remain lowered or-extended? "Therefore this systemhas for anadditional "object" to provide a landing gear control system Iincludingilofcking meansthc operation ofwhich isgind'ependent of athecondition of the" nun circuit controlflfng theraising and *lo'wering' of"the scen 'landing'gearr'systems"were "designed with-an ob- It isanother object "towprovide such a syste mu in which, while tthe-ilocking .means remain independent of the fluid circuit solaslto providethe v proper locking-.efiecty the unlocking of suchlocking-meansis-effectedby .the controlmeans governing the fluid circuit controllingthe raising and lowering of the gear. I .7 It ishanl additionaltobjectto providela landing geansysteminwhich' the unlocking, of the locking,

means is efiected before-,the. application of the powerstroke toreffecting-t raising-orlowering of themlandin ear-1S0. thatkundue strainson the locking: means are-avoided; V

Anothenobject-of theepresentninvention resides in thefactthatltheimotive. pressure that moves the. landin -V; gear towardeither. of its extreme positions. that. is.eitheri itsretracted orlowered position, remainsmappliedi after the. fulfillment of .thismovement thusrelievihg the mechanical locking i meanstandl contributingto V the main--v tenanceof the gear in the. position thus. reached;Specifically? theretore .the.present invention has for an :object.toeprovidenaretractable landing gear-system in whichthe movement of thegear between its. extreme positions is controlled through; ahydraulicrelay, the actuating member ofwhich has an initial phase of movementtermed (the approaching phase which does not afiect the relaybut 7 whichdoes unlock the locking means.

specifically, .the .relay. constitutes a suitable valve .thisipiston.

Morespecifically the piston operative on the relay through a pushermember normally spaced from thewvalve: so wthatthe vmovement of thepushing member constitutes the. approaching phase:

"Fomamturther: specific object the rod of the piston: -controlling;-;the relay 'is associated ;with

camsmeans operative upon la member controlling theunIockinQxof'YtIierlockingr meansi which cam i imember" isi operative"during}: the approaching movement or the'.-.-pistonr toward the relaycontrolledthereby:

In an: alternative. arrangement the rod of i this control 'piston isdirectly connected to the-mem- '1=bercontrolling 'theunlocking" of thelocking 'means. a l

In the present system the power 'fon'moving thelanding gear' isprovide'd rby' two hydro-pneumatic" accumulators each" primarilyoperative te -upon one-' halr-ct the gear; Thetworaceumulators aremounted in series with a pump and their capacity is such that withoutthe intervention of the pump, as to. effect two consecutive operationsof the gear, for example a retractionrmovement and an extension orlowering movement.

This arrangement thereby providing a system in which the conduits orpiping connecting the accumulators, the accumulator with the source, andthe accumulator with the pump may be of small diameters. r

Further and more specific objects and advantages of the presentinvention will be apparent from the following description taken inconnection with the accompanying drawings in which- Figure 1 is adiagrammatic view illustrating an embodiment of the control system forthe landing gear,

Figure 2 is a partial view on an enlarged scale and partly in section ofone-half of the system, Figure 3 is a diagrammatic illustration of theconnection between the hydraulic relayand the mechanical locking means,and l y Figure 415a view similar to Figure 3 illustrating amodification.

In accordance with the invention th retractable landing gear may be ofany conventional type providingthe operation thereof is effected byhydraulic jacks. J T l In the drawings each half of the landing gear ismovable through a double-acting hydraulic jackgdenoted respectively at land l Y Each of these jacks is fed by a hydro-pneumatic accumulatordenoted respectively at 2, 2 The components relating to the right halfof the landing gear system being identical with and similarly disposedto those components relating to the left half of the system, they are,for the most part, indicated on the drawing by the same referencenumerals followed by the index letter a.

The cylinder of the hydraulic jack I has a piston 3 therein whichdefines in the jack two chambers 4 and 5. The actuation of the half ofthe landing-gear, for retraction as well as for lowering, is effected bythe piston rod 6.

The hydraulic jack 1 is fed by the hydropneumatic accumulator 2, throughdistributing relays! and 8. The distributing relay 1 is connected to thechamber 4 by a pipe 9, and the distributing relay 8 is connected to thechamber 5 by, a pipe Hi. The distributing relay 1 places the chamber 4in communication either with the hydro-pneumatic accumulator 2, or withthe tank ll, according to the position of a controlling 'de- .vice notedgenerally at I2 and disposed within reach of the pilot, and,simultaneously, the distributing relay 8 places the chamber 5 incommunication either with'the tank H or with the hydro-pneumaticaccumulator 2.

Fromthe hydro-pneumatic accumulator 2 extends a pipe l3 for feeding thedistributing relay 8. From this pipe I2 extends a pipe [4 for feedingthe distributing relay 1, and a branch pipe 7 i5 for conveying'fiuidunder pressure to the controlling device l2. In the system theaccumulators 2 and 2 are maintained under pressure by a pump l6, suckingliquid from the tank I I and discharging the liquid under pressure intoa pipe H; the connection between this latter and the accumulator 2including a suitable one-way valve device l8. On pipe I! is provided anautomatic by-pass device I8,- known per se and preventing the pressureof the acccumulator 2 from exceeding a given value.

The accumulators 2 and 2 are of such capacity :as to assure, withoutrecharging, two successive L operations of the gear, for example oneretraction 4 and one lowering. Pipes I5, l and I1 may therefore be ofsmall diameter.

-1'Ihe controlling .device I 2 is fed fromthe pipe l5, from whichextends: a pipe" l9 dividing into two branches and 2| which respectivelypro- "vide communication with the two distributors 22 and 23, of thecontrolling device I2.

' The controlling device [2 includes a handle 24 having two arms 25 and26 by which the distributors Hand 23 may be selectively actuated. Thedistributor 22 is devoted to the retraction of the landing gear, and thedistributor 23 to its lowering. A pipe 21 sub-divides into pipes 28 and28 'and constitutes the flow transmitter between the distributor 22 andthe distributing relays 8 and 8 A pipe 29 sub-divides into two pipes '30and 30 constituting the flow transmitter between the distributor 23 andthe distributing relays I and 1 The emptying of, or return flow from,the various devices is effected through a pipe 3| of large section whichis connected-to the tank II. To pipe 3| is connected a pipe 3t extendingfrom the distributing relays! and 8, a pipe 33 extending from'thecontrolling device l2 and a pipe 32 extending from the distributingrelays 1 and 8?. e The construction of one of the distributing relays,for instance the relay 1, will now be de scribed with particularreference to Fig. 2. The distributing relay 1 includes a cylindricalportion 34 in which a piston 35 is slidably mounted so asjto define twovariable volume compart ments therein, denoted respectively at 36 and31. Av pipe 30 extends into and provides fluidfiow into the compartment31; This pipe preferably extends through a ring 38 limiting the movementof the piston 35. The rod 39 of the piston 35 passes through the bottom40 of the cylindrical portion 34 through suitable packing 4l. The piston35 is alsoprovided with suitable pack ing, 42. A spring 43, abuttingagainst the other end 44 of the portion 34 reacts against the face of'piston35 directed towards the compartment 36. The said face of thepiston carries a buffer 45 cooperating witha rod 46 which, ismovablethrough an opening 41, provided in the end 44 of thecylindrical body 34.This rod 46 is provided with a collar or flange 48 subjected to theaction of a spring 49 controlling a hydraulic relay ,5!) of a type knownper se.

This hydraulic relay 50 includes a valve 5| having a hollow body and acap or head 52 cooperating with an apertured diaphragm 53 andcontrolling communication between a chamber 54 at one end of the relay50 and into which chamber fluid' flows from. the pipe l4 and acompartment tured diaphragm member 58. This latter member. 58 is hollowand includes opposite end walls through which the hollow body of thevalve 5| The hollow valve body is provided fluid to flow from chamber 54through theaper- .ture in diaphragm 53 through port 56 through thehollow body out of port 51 through the hollow diaphragm member 58 intothe conduit or pipe 9 providing communication-with the chamber 4 of thejack l. -A further compartment 59 is provided in the valve 50 betweenone-end face of the hollow member 58 and the end wall 44 of theQcylindrical portion 34.. The spring 49 is disposed within thiscompartment and bearsagainst the flange or col1ar'48 and thiscompartment 59 is is slidably mounted l innfi connectedbymeansofimcondui i the -correspcndingmmnpartmen .ottherrelam and whichcompartment: M3; eimicommunzicire tion through thepiper-=32:withr:.the:retumspipe 3 1 to: "the tank Ii L: A- coil sprihgulis. pravfded :L'lnr.

the chamber" 54 which ears: thcrendl oi the relay into rwl'i-ichthem-pipe: lifextends'sand the adjacent faicei. ofsithe head for "tilofithe valve-5 k i I v r The distributingmelay @Bziis af -1 pcanstmgation to that bf distributingfaarela 1.1 its. cylindrical body 62 isa-pistomii avingamodufl and abufier 1 65 acting onira rod 6513 pemtingwith arvalve ii'I simiianZto t valiverfit, cooperating with awalvwfi Isimilar to thewal ve '1; The-pipe 3 commu nica ing with the-9mm!partment; :68- of-rfthehydraulfd relay fifl'p and:the pipe 1 0:extendingifrom thespacewenclo'sed bwthehollow diaphragm fl-0.

' The distributors :22 and- 2 control-device l2," are i also oil th typewhich has just been-described. 'The val ve" *headz or reap: 1-1 of thedistributor '2 2 controlszcommunicationrbetween-the pipe and: the pip'e2'1' andl thereby ment of retraction or of iprotractionn Thisunlockingoccurs during the phase in which" the' -pis ton of a"distrib'utingrelay, 'for="example, the piston 3 5, approaches towards}the =rod 16. For this purpose, a substantial play or'space isinten=tionally provided between the. front face-of the buffer 45 and the"adjacent piece off therod W; The buffer 45' andthe rod rjflfiare' showrrin their extreme positions in Figure 2 ineonnection' with thedistributing-relay l'.

The connection between the 'distributingrel'ay and the. icorrespondingmnloc kingjgdevice. is; further such, that whenit'hegunlockhig;isgetfected; during the approachingstroke of'the piston35 or 6.3, the unlocked conditionrremains duringgthe subsequentmovementlof the piston which. controls the. operation of the hydraulicrelay 7 By wayof' example Fi'gl3'jshows .a-(mechanical connection whichcan be. used-for .the control of one .of the locking devices of.thelanding. gear; .for

instance loiljthe devicegfor, the locking in. the..- re- 1 tractedposition or up-lo'cIgL. iThi'seconnection is operative from.amdistributinglrelay for .ex-

am le the distributing relay 1."; The pistongrod 39 ofthisdistributiiigprel'ay, onnecte'dithrough an articulation ,8-lj.l tfoane d; hides-J1 Land; 84.

constituting the connectedfby a pipe 2 This rod,.includes..-a.;proiection 5 or. ,campiihe shape of whichisadvantageously that: shown on Fig. 3, that is to say, it includes afacen86 parallel to the axis. of the rod-Mandarin inclined face, as at87-, between face,ai andthimodpmDer. With ,these faces .86 and 81eooperatesairoller on cam.- vfollower 88 mounted-(on theupper endTOivBn-I'Od 89 --which slidesin a: nxed guideefl. Theizother aqua-sacsarm. Sit or: awaidcuble-armed fierce" 9.2. 'zr'rotatablyi mounted oniazpivotrfli the :other: arm- 94 forms,

withsmpin "95 havingaza. beveled 96, the lock; proper; Thepinv 951s:slidably mounted ina bore prouidedrinvtheilandingagear and is urged up.wards-by a-"springila. Arspringfifi acting against the arm 94constantlyxurgesthe ro11er:88:toward theraxisszoficrod flz. i

In. positionnshownwin E-igs. 1 and 2, the landing;- gear isminxitsiretracted position. The chamber :5L-fof the hydraulics-jack is inpermanent. connection by pipe I 0 the hydraulicrelay 8,i-and thetpipec131,; withuthe hydro-pneumatic accumulator-1 2.1sonthat their eventualdilatations of the liquid1'take ,-place freely:- The piston 63: ismaintained'xinits -operative'iposition; that is to saypinpomtioniforactuating'the hydraulic. relay 8, due tonthezcpressure which exists:constantly .in the rear ,7 chamber oil .the cylindrical portion 62innwhich-apressurew emanates from the. flow of fluidithrough pipe-15;.thence through at. this time distributor 22,;iwhosesrodl2 is thendepressed, thence through conduits 21, 28 into said rear ehamben. Onthe-contrary, the piston 35 of the distributing relay 1: is appliedagainst the ring 38, the chamber 31 being then connected toathereservoir-H through itheapipes 30 and 29, the distributor 23,:the -pipe\80,.: the chamber :11 of the distributor 22, and pipes' 33and 3l Inthis position ot piston 35," the gear is locked. in. itsretracted'position by 'cooperation 'of the double armed lever 92= and the M1195.This locking remai'ns evenrifdamageoccursin the hydraulic circuit:operatingv the gear; as the position of pistonr3i5 -WhiOh 8;SSu13BSFthelocking is that which correspondsto thelacl'r of pressure inthechamher-=31.-

For lowering'the gear, it is only -necessary' to reversethe movement ofhandle 24 in order that the=arm-25' 1eaves therod l2 and the arm 26connects thispipe 21 with the pipe 33 issuing through-3 I" tothe tankII. The pressure behind the piston Bidis'appearswand the piston takes upits inoperative positiomthus putting into clutching' conditiontheqdevicefor-the locking-of the gear in thejlowered position; The valve 61 isapplied on its seat, and the chamber 5, previously connected with'thepressure pipe 13 through the 'distributingrelayt, is connected to thepipe 32f returning to the tank; I l.

Simultaneously, thekactuation of the rod. 19 has connected the chamber31 of the distributing relay] with the pressure pipe I5 through thePipes-.M-and 29;.th'e distributor 23,, and the pipes 2l.'-.andji9,.,Atithe same time, the connection which. wasnpreviously establishedvbetween the chamberj'l and-.the tanke-and whiclrallowed theliquidncontainednin this .chamber to dilate .freely without the positionof. the pistoniifi being 'changed jthereby is cut off by the applicationiofaithe endnof the rodu'l-anagainst the open end .ofo the valve of thedistributor .23.

Whenatheuchamberfil is under pressure, pistoni .35 moves; to theleftagainst the action, .of

spring 473, .During the initial phase of? this moveyment. thetbufierii-approaches the rod 46 and simultaneously roller. 88 rollslontheinclined face 81 of the cam. so=that the doublezarm'locking lever-1 iserotated :byythe action; of 'spring laon Y end of this ;;rod isfin;.per;manent;contactvwith an Qarmn 94,-; thus disengaging the locking5 pin. 1 95,

thereby unlocking-the landing gear from its retracted position. Up tothe moment that the gear is unlocked, there has been no hydraulic forceacting thereon to urge the same to lowered or extended position so thatthe means for looking the gear in retracted position have not beensubjected to any undue efiorts. 1

When the buffer=45 comes into contact with the rod 46, the gear isunlocked, and the continuation of the movement of the piston 35 nolonger influences'the position of this locking device. Upon continuedmovement of rod 46, the hydraulic relay 50 is brought into operation, inthe customary manner, that is, the pipe 9, formerly connected with thetank through the hydraulic relay 50, the pipe 60, the hydraulic relay 69and the pipe 32, is isolated from the tank, and, on the contrary, isconnected with the pressure pipe I4 through the said hydraulic relay 50.The pressure which thus arrives in the chamber 4 of the hydraulic jack Icauses the lowering of the landing gear. When this latter reaches itslowered position, it looks itself automatically, because the device forthe locking in lowered position or down-lock is then back in its activeposition.

The retraction of the gear is carried out by an operation inverse to thepreceding one, and the inverse phases occur.

In Fig. 4 is shown a modification of the mechanical connection betweenthe hydraulic relays I and 8 and respectively the up-lock and thedown-lock of the gear. In this modification, the locking of the gear inits retracted position is assured by a hook I hinged at IOI and withwhich is engaged a pin I02 carried by a lug I03 0n the body I04 of theshock-absorber. This latter is rotatably mounted about axis I05. Thehook I00 is maintained in locked position by a spring I06. To the hookI00 is attached a pulling wire I01 connected at its other end tothe rod39 of the distributor relay I. -When this distributor relay is actuatedto lower the gear, the hook I00 is first moved against the action of thespring I06 and the gear is unlocked. The release position of the hookI00 and the pulling wire I 01 is shown in dotted lines. The releasingmovement of the relay I in Fig. 4 is to the right and the continuedmovement of the piston rod 39 has no further efiect on this up-lockdevice except that it pulls still more the spring I06. During the nextretraction ofthe landing gear the hook I00 is returned to its activeposition by the action of this spring I08, so that when the gear reachesits retracted position it locks itself automatically by the snapping ofthe pin I02 behind the bevelled face I08 of the hook I00.

In this modification, the locking of the gear in the lowered position isassured by a hook I09, ro tatably mounted around an axis I I0intermediate the ends of the hook, and which hook cooperates with a pinII I carried by one of the elements I I2 of a folding strut Il3interposed between the body I04 of the shock-absorber and a fixedpartII! of the fuselage. In order to control the locking and the unlockingof the gear, a pulling wire II4 attached at one end to the free end of ahook I09 and at its other end the wire is connected to the rod 64 of thedistributor relay 0. A spring H constantly urges the hook I09 to lockingposition. During the operation of retracting the gear, the wire II4,during the approaching stroke, that is the initial phase of movement ofpiston 63, swings hook I09 to the released position and the gear isunlocked for movement from its lowered position. The release'position'ofhook I09 and its pulling wire I-I4-is shown in dotted lines in thedrawing. The continued movement of the rod 64 takes advantage of theresilience of the spring H5. When the gear is'next being lowered thehook I09 is returned -toit's active or locking position by the springII5 andswhen the-gear has reached its lowermost position, the hook I09automatically locks itself by a snapping engagement between theengagement of the bevelled face N6 of the hook I09 over thepinIIL-Having now described my invention, .what I claim, and desire to secureby Letters Patent, is: 1. In a retractable'landing gear for aircrafthydraulic jacks for raising and lowering the same, a fluid circuit foreffecting the movement of said jacks including a source of fluid underpressure, operating valve means in said circuit between said source andsaid jacks and including separate valves controlling the admission offluid to opposite ends of the jacks to respectively move the jacks inopposite directions upon alternate operation thereof, each of saidoperating valve means including a movable member controlling themovement of the valve, said circuit further including means coupling theoperating valvemeans associated at the same end of different jacks foractuation inunison so that the operating valve means are operable inpairs responsive to the movement of pairs of said movable members,selective energizing means including an element movable between two.extreme positions for selectively moving pairs of said members, saidmembers having an initial phase of movement not affecting said valvemeans but operable upon continued movement to actuate said valves,separate latching means for respectively immobilizing the gear in' itsraised and lowered positions, movable mechanical connections extendingbetween said-members and said locking means and operable upon movementto unlock the same, the movement of said connections being responsive tothe initial movement of said members whereby upon selec tive actuationof said energizing means pairs of said members move and during initialmovement ,unlock the locking means associated therewith and uponcontinued movement actuate the associated operating valves to permitfluid flow to the end of the jacks associated therewith whereby thejacks raise or lower the gear depending upon the positionto which saidenergizing means is moved. v

, 2. In a retractable landing gear for aircraft as defined in andbyjclaim 1' in which said mechanical connections include a rod coupledto said member for movement therewith, a cam carried by said rod andwhich said locking means includes aj'cam follower and means responsiveto the movementof the follower to permit unlocking of the lockingmeans.

3. In a retractable landing gear for aircraft as defined inand by claim1 in which said lockin meansincludes a pivoted latch and in whichsaidmechanical connections include cables respectively connected betweensaid latches and said members and responsive for moving said latches tounlocked position upon initial movement of said members. v

4. In a retractablelanding gear, a hydraulic jack, an accumulatoradjacent said jack, hydraulic connections between said jack and saidaccumulator, operating valve means in said conmotions to enable theaccumulator when charged to operate thejack under control oftheoperating valve means, hydraulic actuating valve meansv means, lockingmeans for retaining said gear in a fixed position, said operating valvemeans including a member movable responsive to fluid flow through saidpiping independently connect-- ing said actuating valve means with saidoperating valve means, said member being capable of an initial movementduring which it does not affect said valve means, and a subsequentmovement during which it affects said valve means to permit fluid flowfrom said accumulator to said jack, a mechanical connection between saidmember and said locking means and movable in response to the initialmovement of said member to unlock said locking means whereby uponoperation of said actuating valve means said member moves to initiallyunlock said locking means and thereafter to control said operating valveto permit fluid flow from said accumulator to said'jack to move saidgear.

5. In a retractable landing gear for aircraft hydraulic J'acks forraising and lowering the gear, mechanical means for locking the gear inits raised and lowered positions, a fluid circuit for effecting themovement of said jacks and including accumulator means, operating valvemeans between the accumulator means and the jacks, said operating valvemeans including separate valves controlling admission of fluid toopposite ends of the jacks, a fluid pressure responsive memberassociated with each valve and movable to operate the same, said memberhaving an initial phase of movement not affecting the valve, conduitsproviding communication between said accumulator and said operatingvalve means and through which fluid under pressure flows to move .saidmembers, additional valve means interposed in said conduits controllingfluid flow therethrough, said valve means being alternately movable soas to alternately control flow of fluid to alternate members to effectmovements thereof for alternately controlling the admission of fluid toopposite ends of said jacks, means for imparting alternate movement ofsaid last-named valves selectively and mechanical connections extendingbetween said members and said locking means, said connections beingoperable upon movement of said members to unlock said locking meansduring initial movement of said members and before said members actuatethe valves associated therewith to permit fluid flow to the jacks.

6. In a retractable landing gear a pair of hy- 10 draulic jacks, aretractable landing gear member associated with each jack and raised andlowered thereby, pivoted self-locking latches automatically operable tolock said landing gear members in their respective raised and loweredpositions, a control circuit for said jacks including a pair ofaccumulators, branch piping connecting the accumulators with theopposite ends of each jack, an operating valve means in each branch ofsaid piping, said valves being normally closed and operable when openedto permit fluid flow from said accumulators to said jacks, pipingconnecting the accumulators, branched piping communicating with thepiping connecting the accumulators intermediate the same, a controlvalve means in each branch thereof, said operating valve means eachincluding a cylinder and a piston movable to open the valve, pipingconnecting said cylinders'behind said pistons with the control valvemeans in said second-mentioned branched piping, additional pipingconnecting said control valve means in circuit with said accumulators, areservoir and a pump communicating with said pipe to maintain pressurein said accumulators, said control valve means each including a normallyclosed valve preventing fluid flow therethrough, a reciprocable memberto open said valve, and means normally holding the reciprocable memberin inoperative position, a movable selector element cooperable with saidreciprocable members and movable in selected positions to alternatelyand selectively move said members to control said valves and therebyfluid flow to said pistons to automatically open the valves in theoperating valve means to permit fluid flow to said jacks and mechanicalmeans directly connected to said pistons and operable upon said latchesto unlock the same during initial movement of said pistons. RENE LUCIENLEVY.

REFERENCES CITED The following references are of record in the file ofthis patent:

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